Photothermal transducing spectroscopic analyzer

ABSTRACT

In a photothermal spectroscopic analyzer in which a probe light is made to fall on a thermal lens produced in a sample by an input of an excitation light and the sample is analyzed in accordance with a change of the probe light which is caused by the thermal lens, a light source of excitation light is composed of semiconductor laser light emitting means, and a light source of the probe light is composed of another semiconductor laser light emitting means, and furthermore a condenser lens for focusing the excitation light upon the sample and a condenser lens for focusing the probe light upon the thermal lens are configured by a common condenser lens. Such a photothermal spectroscopic analyzer according to the present invention satisfies all the requirements of small size, low manufacturing cost, high sensitivity, high precision, maintenance free performance, short start-up time, and automatic measurement for such a device as to perform POC analysis.

TECHNICAL FIELD

The present invention relates to a small and inexpensive photothermalspectroscopic analyzer which analyzes a microvolume sample in highsensitivity by using a semiconductor laser.

BACKGROUND ART

The importance has been noted of carrying out analysis and measurementsright at the site or in the vicinity of the site where analysis andmeasurements are required (hereinafter referred to as “POC (point ofcare) analysis etc.”), such as analysis for bedside diagnosis whichcarry out measurements necessary for a medical diagnosis at thepatient's side (POC analysis), analysis of toxic substances in rivers orwastes carried out at the sites, that is, on rivers, waste disposalcenters and the like, and tests for contamination carried out at thesite of cooking foods, harvesting crops, or importing foods. Then,importance has been attached to the development of detection methods anddetection apparatus which are applied to such POC analysis etc. inrecent years.

In the detection method and detection apparatus which are applied tosuch POC analysis etc., it is required that an analysis is simple,brief, and inexpensive. Furthermore, in a medical diagnosis or anenvironmental analysis, in order to perform comparison with a referencevalue, which a national government defines, in sufficient precision, itis generally required that a high sensitivity analysis is performed.

Recently, μ-TAS (micro total analysis system), which has a groove, whosedepth is from tens μm to hundreds μm, on a flat glass or silicon chip atthe largest 10 by 10 cm square in dimensions, or a few by few cm squareor smaller in dimensions, and performing all of reactions, separation,and detection for a short time in this groove has been actively studied(for example, Japanese Patent Laid-Open No. 2-245655).

The adoption of μ-TAS has advantages that the amounts of samples,reagents for detection, and waste materials and waste fluid ofconsumables used for the detection are reduced, and necessary detectiontime is also short in general.

In addition, a method of forming a chip with resin(R. M. Mccormick etal., Anal. Chem., vol. 69, 2626–2630, 1997, Japanese Patent Laid-OpenNo. 2-259557, and Japanese Patent No.2639087 (registered on Apr. 25,1997 for Shimadzu Corp.)) for developing an inexpensive disposable chipis also proposed.

However, since optical path length is dozens to hundreds μm that is 1/10to 1/100 of that under usual conditions, in inverse proportion to it, itis required that the sensitivity of a detection apparatus is 10 to 100times as high as that under usual conditions when optically detecting ameasuring object in μ-TAS.

Up to now, a photoinduced fluorescence method or a chemiluminescencemethod which use a luminescence phenomenon from a measuring object andanalyze the concentration and the like of the measuring object from thequantity of light of its luminescence have been adopted in a highlysensitive apparatus which optically detects the measuring object.However, the photoinduced fluorescence method has a problem thatbackground becomes large by fluorescence from other objects than ameasuring object in practical samples with many impurities since thelight with wavelength near an ultraviolet ray is generally used in manycases as a light source to excite the measuring object. In addition,since a measuring object is limited to fluorescent material, it is notgeneral as a detection method in clinical inspection such as an analysisof blood components.

Furthermore, although there is an advantage that the chemiluminescencemethod does not need a light source for excitation, it has notversatility similarly to the photoinduced fluorescence method.

On the other hand, as a general detection method, there is an absorptionphotometry which analyzes the concentration and the like of a measuringobject by the absorbance of light.

Since the absorption photometry is a method applicable to any object solong as it absorbs the light with wavelength for excitation, it has beenused as a detection method with very high versatility.

In addition, since the sensitivity of absorption photometry is low incomparison with the photoinduced fluorescence method orchemiluminescence method, the concentration sensitivity of theabsorption photometry has been increased by providing dozens mL ofmeasuring object, which is sufficient quantity, and making optical pathlength be 1 cm which is long. However, in μ-TAS, since the optical pathlength becomes 1/10 to 1/100 as described above, the absorptionphotometry has a problem that sensitivity is low when it is applied toμ-TAS although it is a common and highly versatile detection method.

As detection methods which solve the above-described problemssimultaneously, photothermal spectroscopy methods are mentioned. Thesedetection methods are methods of utilizing a phenomenon of a measuringobject absorbing light that is usually a laser beam with the samewavelength as the absorption wavelength of the measuring object(hereafter, this light will be described as excitation light), andemitting heat (photothermal effect) to a surrounding solvent followingrelaxation process, and analyzing the concentration and the like of themeasuring object by measuring the heat. The photothermal spectroscopymethods have a characteristic that the amount of absorption of light,i.e., the heat can be directly measured against the absorptionphotometry indirectly measuring the amount of absorption of light as theamount of decrease of transmitted light.

Among such methods, a thermal lens spectrometry of using a thermal lenseffect is also known as a most sensitive detection method. When a laserbeam is focused with a condenser lens and is incident on a measuringobject, heat generates near its focus (focal point) by theabove-described photothermal effect, and temperature at the point rises.Since the spatial intensity distribution of the laser beam in theabove-described focus is generally a gaussian type, the heatdistribution, generated in proportion to the intensity distribution, andthe temperature distribution generated as its result also becomegaussian types. Then, since a refractive index of a solvent decreases astemperature rises, the refractive index distribution becomes a reversalgaussian type. Since this refractive index distribution can be assumedto be equivalent to a concave lens optically, and such refractive indexdistribution is called a thermal lens. This thermal lens spectrometryhas another excellent characteristic that this method has 100 times ormore of sensitivity as high as that of the absorption photometry inaddition to a characteristic that a measuring object should just absorbthe light with wavelength for excitation similarly to the absorptionphotometry.

In such a thermal lens spectrometry, there are a single beam method ofperforming both the excitation and detection of a thermal lens with onelaser, and a double beam method using two separate lasers for excitationand detection of a thermal lens. Although the single beam method ischaracterized in simple structure and easy optical adjustment, itbecomes difficult to set the optimal optical configuration for each ofexcitation and detection since one laser performs both the excitationand the detection of a thermal lens, and sensitivity is low incomparison with the double beam method.

On the other hand, since the double beam method can use separate lasersfor the excitation and the detection of a thermal lens, it is possibleto set the optimal optical configuration for each, and to realize highsensitivity. Then, many examples of such a double beam method are known.

In addition, there is an example where highly sensitive measurement wasperformed with applying this double beam method to μ-TAS (Manabu Tokeshiet al., J. Lumin., Vol.83–84, 261–264, 1999). In this double beammethod, an Ar ion laser is used as an excitation light source, and ahelium neon laser is used as a detection light source (hereafter,detection light is described as probe light), after making these twolaser beams coaxial, the beams are led to a microscope, and are focusedwith an objective lens on a sample in a groove engraved on a chip.

In such a conventional thermal lens spectrometry, a gas laser such as anAr ion laser or a helium neon laser, a dye laser excited by a gas laser,or the like has been generally used. However, presently, when anapparatus generating the above-described laser beams is actually used,the apparatus is large-sized, large-scale cooling means such as watercooling means is needed at the time of a high-power output, and theapparatus becomes very expensive. In order to solve those problems,several examples that use semiconductor lasers and are comparativelysmall systems are known.

First, examples using the single beam method will be described. InJapanese Patent Laid-Open No. 4-369467, a semiconductor laser is used,further, in order to shorten distance between a sample and a detector,an optical system which detects a focus error of reflected light isadopted, and the miniaturization of an optical head is realized.

In addition, there is also an example where an apparatus which is smalland portable is realized with the single beam method using thesemiconductor laser with a wavelength of 670 nm, and further, an entiresystem is miniaturized by connecting a sample and a detector with afiber (KIM S-H, Bull. Korean Chem. Soc., Vol. 18, 108–109, 1997, and KIMS -H et al., Bull. Korean Chem. Soc., Vol. 17, 536–538, 1996).

On the other hand, there is also an example using the double beammethod. For example, phosphorus was analyzed by making a semiconductorlaser with a wavelength of 824 nm be an excitation light source, and thedetection limit of 0.35 ppb was obtained in an aqueous solution (K.Nakanishi et al., Anal. Chem., Vol. 57, 1219–1223, 1985).

FIG. 7 shows a structural diagram explaining the construction of aconventional photothermal spectroscopic analyzer using the double beammethod which uses semiconductor lasers. In such a photothermalspectroscopic analyzer, excitation light is outputted from asemiconductor laser beam-emitting apparatus 71, and after being focusedwith a lens 72, the light is focused with a condenser lens 73 on asample in a glass sample cell 75 with the optical path length of 1 cm.Then, a thermal lens is formed in the above-described sample where theabove-described excitation light is incident.

In addition, probe light outputted from a helium neon laser apparatus 81is led to the sample cell 75 by a beam splitter 74 in collimated lightcoaxially with the above-described excitation light. The probe lightincident on the above-described thermal lens is given a thermal lenseffect in the sample cell 75, reflected by a mirror 76, and focused by acondenser lens 77, and thereafter, the probe light is received by aphotodiode 80 through an excitation light cut-off filter 78 and apinhole 79, and is given a signal analysis.

Similarly, there is also an example where the detection limit of 8×10⁻⁵M is obtained with using Nd³⁺ aqueous solution and a 10mW excitationlight output by using a GaAlAs semiconductor laser with the wavelengthof 795 nm as an excitation light source (D. Rojas et al., Rev. Sci.Instrum., Vol. 63, 2989–2993, 1992).

Furthermore, in order to improve sensitivity, there is also an examplewhere the absorbance limit of 1.1×10⁻³ was obtained in an aqueoussolution by increasing an output of excitation light to 100 mW by usingan array type semiconductor laser with the wavelength of 818 nm (CladeraForteza et al., Anal. Chem. Acta Vol. 282, 613–623, 1993).

However, each of these three examples uses a helium neon laser, which iscomparatively large-sized and expensive, as probe light, and hence, thisis not an apparatus composed of only semiconductor lasers.

As mentioned above, the photothermal spectrocopy method is highlysensitive in comparison with the absorption photometry which analyzes asample by using the absorption of light similarly, and it is possible tominiaturize a photothermal spectroscopic analyzer to some extent bymaking a semiconductor laser be an excitation light source.

However, the above-described conventional technology has the followingproblems when realizing the photothermal spectroscopic analyzer which isequipped with high sensitivity, high accuracy, maintenance-freeperformance, short start-up time, and high reliability and operabilityin addition to the natural requirements for performing a POC analysisetc., that is, small dimensions for portable use and inexpensiveness.

First, as mentioned above, the single beam method using a semiconductorlaser has an advantage that the adjustment of an optical system becomeseasy. However, since its sensitivity is low in comparison with thedouble beam method, its sensitivity is insufficient in many cases as amethod of using this in the case, where high accuracy is required indata, such as medical diagnosis or an environmental analysis.

Next, in the conventional double beam method, only an excitation lightsource is composed of a semiconductor laser, and a helium neon laserthat is large-sized and expensive is still used as a probe light source.In such a case, it is reported that the minimum size of an opticalsystem except the light sources is 30 cm×30 cm. However, since the sizeof the helium neon laser which is a light source is usually 5 cm dia.×20cm long, the apparatus become large-sized when this is added (D. Rojaset al., Rev. Sci. Instrum., Vol. 63, 2989–2993, 1992).

In addition, since a large-sized laser such as a helium neon laser isused, a light source and an optical system cannot be integrated and thelight source and optical system are separately fixed on an opticalbench, and hence, carrying is impossible. Furthermore, a gas laser alsohas troubles such as necessity of a high voltage power supply.

Moreover, up to now, in order to obtain sufficient measurementsensitivity, it is necessary to make distance from a sample to a devicecorresponding to a pinhole be 1 m or more that is long. Thus, since longdistance is necessary for leading the probe light, which is given thethermal lens effect in the sample, to a pinhole, the miniaturization ofthe whole optical system is disturbed due to the restriction of suchdistance from the sample to the device. If this distance is shortenedwithout design, it is expected that it leads to sensitivitydeterioration.

In addition, there is an example where the above-mentioned distance isshortened by not using the pinhole method as the light-receiving methodbut adopting a method using an optical system which directly detects afocus error. However, there is no report of affirming that thesensitivity of this method is superior to that of the pinhole method(Japanese Patent Laid-Open No. 4-369467 applied by YOKOGAWA ELECTRICCORP.).

Furthermore, as a method of improving the sensitivity of a thermal lensspectrometry, it is commonly known that it is important to optimize thedegree of focusing to the depth of a sample cell (namely, optical pathlength) and to adjust a focal point of probe light with shifting thefocal point from a sample (Thierry Berthoud et al., Anal. Chem., Vol.57, 1216–1219, 1985). However, since the optimal degree of focusing orthe optimal focal point of probe light depend on a plurality of otherparameters and it is not possible to theoretically analyze all of thoseparameters systematically, there is no report of the theoreticalanalysis of the optimum values at the time of raise the degree offocusing, up to now.

In particular, since the optical path length becomes short in μ-TAS, itis expected that it is necessary to raise the degree of focusing to someextent. In order to raise the degree of focusing, it is needed to makethe numerical aperture of a condenser lens large. Since a focal lengthbecomes short to several cm when the numerical aperture is increased, itis not possible to make the excitation light and probe light be coaxialdue to a spatial limitation in the case that the degree of focusing andthe focal point of the probe light are adjusted by using separatecondenser lenses for the excitation light and the probe light like aconventional way.

Then, it becomes possible to use a condenser lens with large numericalaperture since the excitation light and probe light are focused afterbeing made to be coaxial if the condenser lens of the excitation lightand probe light are made to be common like another conventionaltechnology (Manabu Tokeshi et al., J. Lumin., Vol.83–84, 261–264, 1999).However, there is no report about an adjusting method of a focal pointof probe light at the time of sharing a condenser lens.

In particular, since it is known that the outgoing light of asemiconductor laser completely differs from a gas laser, a simple methodof adjusting a focal point that is suitable to the characteristics ofthe semiconductor laser is needed.

First, the outgoing light of a semiconductor laser is divergent light,and its cross sectional geometry becomes elliptic. Furthermore, if theoutgoing light is focused as it is, the astigmatism that a focal pointchanges according to a cross sectional direction of focused lightexists. Therefore, when using semiconductor lasers as both the lightsources of the excitation light and probe light, it is necessary tocorrect the intrinsic characteristics of the outgoing light of thesesemiconductor lasers.

Thus, in the case of using semiconductor lasers as both the lightsources of the excitation light and probe light, it is necessary toperform the above-described correction and to provide simple andinexpensive means for adjusting a focal point of the probe light.

In addition, when the numerical aperture of a condenser lens is madelarge and the degree of focusing is raised, it is necessary toaccurately adjust the focal points of the excitation light and probelight in a sample cell. Up to now, since the positional relation of afocal point and a sample cell is visually adjusted by using amicroscope, not only a visual alignment error arises, but also analignment error by a measuring operator is included. In addition, it isimpossible to automatically adjust an above-described positionalrelation with a machine in such visual method. Furthermore, an apparatusbecomes large by using a microscope.

In addition, since not only about 10 minutes of time was necessary untilbeing stabilized after switching on a power supply but also mechanicalmodulation means such as a chopper was required for a gas laser at thetime of modulating an output, it was not so easy to performminiaturization and cost reduction.

Furthermore, in addition to these, it is required that a photothermalspectroscopic analyzer used for POC analysis etc. should be strong in anenvironmental temperature change and vibration. Furthermore, it isdesirable that the photothermal spectroscopic analyzer used for POCanalysis etc. does not need a high voltage power supply and is able tobe driven by a dry cell etc.

As described above, in conventional technologies, there is no measurefor the characteristics naturally required of the photothermalspectroscopic analyzer used for POC analysis etc.

Then, a task of the present invention is to provide a photothermalspectroscopic analyzer which is equipped with all the requirements as anapparatus for POC analysis etc., such as small size, inexpensiveness,high sensitivity, high accuracy, maintenance-free performance, shortstart-up time, and possibility of automatic measurement by solving theproblems which the above conventional photothermal spectroscopicanalyzers have.

DISCLOSURE OF THE INVENTION

In order to solve the above-described tasks, the present invention hasthe following construction. Namely, a photothermal spectroscopicanalyzer of the present invention is a photothermal spectroscopicanalyzer in which probe light is incident on a thermal lens generated ina sample by the incidence of an excitation light, and analyzes theabove-described sample on the basis of a change of the probe light bythe above-described thermal lens in that case, and is characterized inthat a light source of the above-described excitation light consists ofsemiconductor laser beam-emitting means, that a light source of theabove-described probe light consists of another semiconductor laserbeam-emitting means, and that a condenser lens which focuses theabove-described excitation light in the above-described sample and acondenser lens which focuses the above-described probe light in theabove-described thermal lens are made to be a common condenser lens.

When the construction is like this, it is possible to make it be a verysmall and inexpensive photothermal spectroscopic analyzer since both thelight source of the above-described excitation light and the lightsource of the above-described probe light consist of semiconductor laserbeam-emitting means. Hence, it is possible to make them be a small-sizedunit whose size is about 15 cm×15 cm by integrating the above-describedlight source and an optical system including the above-describedcondenser lens in stead of separately fixing them on an optical bench.In addition, it is possible to make its construction very strong inexternal vibration by integrating optics such as a light source and anoptical system to make them a unit.

Furthermore, since the life of a semiconductor laser is about 10 timeslonger than that of a gas laser, the interval of maintaining a lightsource can be lengthened sharply.

Furthermore, since the condenser lens which focuses the above-describedexcitation light, and the condenser lens which focuses theabove-described probe light are made to be a common lens, a space formaking the above-described semiconductor laser beam, which are emittedfrom a light source of the above-described excitation light and a lightsource of the above-described probe light, be coaxial can besufficiently secured in comparison with the case where theabove-described condenser lenses are not common like conventionaltechnology. Therefore, since it is possible to use a lens with highnumerical aperture as the above-described condenser lens, and inconsequence, it is possible to tightly focus the above-describedsemiconductor laser beam and to make it incident on the sample, it isalso possible to perform high sensitivity analysis even with μ-TAShaving short optical path length.

In addition, as for the photothermal spectroscopic analyzer of thepresent invention, it is good to set both the beam diameters in focalpoints of the above-described excitation light and above-described probelight, which are focused with the above-described condenser lens, in 0.2to 50 μm.

Up to now, although investigation about the degree of focusing ofexcitation light has been performed qualitatively, the effect ofimprovement in the degree of focusing the probe light has not beenconsidered at all. In the present invention, it was possible to improvethe sensitivity in an absorbance and to remarkably shorten the distancefrom a sample to a device, which was equivalent to a pinhole, incomparison with conventional technology by using a common condenser lensand improving the degree of focusing of probe light.

In conventional technology, even if it aimed at the miniaturization ofan apparatus, the beam diameter of excitation light was about 50 μm at aminimum, and that of probe light was about 200 μm at a minimum. In thiscase, in order to obtain sufficient sensitivity, the necessary distancefrom a sample to a pinhole was about 2 m (Thierry Berthoud et al., Anal.Chem., Vol. 57, 1216–1219, 1985). Since it was expected that thesensitivity would remarkably fall if this distance was shortened, thisdistance restricted the miniaturization of a whole optical system.

In addition, by using a turn-back mirror etc., it is possible to makethe distance from a sample to a pinhole be sufficient length and also tominiaturize an optical system to some extent. However, there is aproblem that there is a bad influence by the pointing noise of a laserbeam in this case. This pointing noise is noise deriving from thefluctuation of an optical axis of a laser beam, and since optical pathlength does not change even if a turn-back mirror etc. is used, thisnoise level does not fall.

In the present invention, it became possible to remarkably shorten thedistance from a sample to a pinhole without spoiling sensitivity bymaking condenser lenses of excitation light and probe light common tomake the beam diameter of a probe light made sufficiently smaller thanthat in conventional technology in a focal point. Since theabove-described distance is short, the pointing noise becomes small inproportion to a shortened part of the distance. Thus, while realizingimprovement in an S/N ratio (Signal-to-Noise ratio) where the pointingnoise is made small with maintaining high sensitivity by improving thedegree of focusing of the probe light, the miniaturization of the wholeoptical system is attained.

Furthermore, the photothermal spectroscopic analyzer of the presentinvention can be configured by comprising at least detection means outof detection means of detecting a change of the above-described probelight by the above-described thermal lens, and transmission means whichis arranged between the above-described sample and above-describeddetection means, for making a part of the above-described probe light,which is changed by the above-described thermal lens, transmit, thedistance in the direction of an optical axis between the transmissionmeans and the above-described sample is set at 10 cm or less when it hasthe above-described transmission means, and the distance in thedirection of an optical axis between the above-described detection meansand the above-described sample is set at 10 cm or less when it does nothave the above-described transmission means.

Since the condenser lens is shared between excitation light and probelight and the degree of focusing of the above-described probe light isimproved, the distance in the direction of an optical axis between theabove-described detection means or the above-described transmissionmeans, and the above-described sample can be set at 10 cm or lesswithout spoiling sensitivity, and hence, it is possible to miniaturizethe whole optical system to the size of enabling carrying. In addition,as the above-described transmission means, for example, a deviceequivalent to a pinhole can be cited.

Furthermore, in the double beam method, since it was known thatsensitivity was improved when a focal point of probe light was shiftedfrom a focal point of excitation light by predetermined distance,adjustment means of the above-described distance was provided. Inconventional technology, since separate condenser lenses were used forexcitation light and probe light, the above-described distance wasadjusted by moving a location of the condenser lens, which focuses theprobe light, in the direction of an optical axis.

However, the above-described technique cannot be applied when acondenser lens is shared between the excitation light and probe lightlike the present invention. In addition, since further addition of alens for adjusting a focal point of the probe light increases the numberof parts and the time and effort of adjustment in relation to it, itbecomes the hindrance of cost reduction. Furthermore, as describedabove, since the outgoing light of a semiconductor laser beam is emittedwith elliptically diverging, a correction mechanism which corrects thisis needed.

Then, the photothermal spectroscopic analyzer of the present inventioncan be equipped with at least one out of a collimator lens where asemiconductor laser beam emitted from a light source of theabove-described excitation light is incident, and a collimator lenswhere a semiconductor laser beam emitted from a light source of theabove-described probe light is incident.

Since a semiconductor laser beam which is divergent light can be broughtclose to collimated light by the above-described collimator lens in suchconstruction, it is possible to suppress power loss in the condenserlens, and to improve the degree of focusing by the condenser lens whenit is brought close to collimated light, and hence, it is possible toimprove the sensitivity of the photothermal spectroscopic analyzer.

Furthermore, it is possible to improve the sensitivity of thephotothermal spectroscopic analyzer since it becomes possible to adjusta focal point of the probe light by providing the collimator lens withshifting it in the direction of an optical axis from a location wherethe semiconductor laser beam becomes the collimated light. Furthermore,since a parts count can be reduced to the minimum, the photothermalspectroscopic analyzer can be made inexpensive.

In addition, since the adjustment of a focal point of probe light is theadjustment of the distance between the focal point of probe light and afocal point of excitation light, it is good to install a collimatorlens, where the semiconductor laser beam emitted from the light sourceof excitation light is incident, so that the excitation light may befocused at a location which is apart by predetermined distance from thefocal point of probe light.

Furthermore, the photothermal spectroscopic analyzer of the presentinvention can be configured so as to be equipped with focal pointadjustment means in at least one collimator lens out of theabove-described collimator lenses for adjusting a focal point of theabove-described semiconductor laser beam by changing the distance in thedirection of an optical axis between the collimator lens and theabove-described light source.

In such a construction, when the above-described semiconductor laserbeam-emitting means is exchanged by its life etc., an error derived frominter-lot difference of an angle of divergence or wavelength can beadjusted, or when the above-described angle of divergence from theabove-described semiconductor laser beam-emitting means changes withtime, it is possible to perform adjustment and optimization.

Furthermore, the photothermal spectroscopic analyzer of the presentinvention can be equipped with rounding means between at least either alight source of the above-described excitation light or a light sourceof the above-described probe light, and the above-described condenserlens of bring close the cross sectional geometry of the semiconductorlaser beam emitted from the above-described light source in the shape ofa perfect circle.

In such a construction, since it is possible to bring the crosssectional geometry of a semiconductor laser beam close to a perfectcircle from an ellipse, it is possible to eliminate anisotropy of thecross section (cross section along a plane perpendicular to thedirection of an optical axis) of beam diameter in a focal point.Therefore, since the beam diameter can be specified uniquely, theoptimization of the beam diameter becomes easy.

Furthermore, the photothermal spectroscopic analyzer of the presentinvention can be equipped with astigmatism correction means between atleast either a light source of the above-described excitation light or alight source of the above-described probe light, and the above-describedcondenser lens for reducing the astigmatism of the semiconductor laserbeam, emitted from the above-described light source.

In such a construction, since it is possible to correct the astigmatismthat a semiconductor laser beam originally has, it is possible toeliminate the anisotropy in the cross section of beam diameter in afocal point. Therefore, since a focal point can be specified uniquely,the optimization of the focal point becomes easy.

Furthermore, in the photothermal spectroscopic analyzer of the presentinvention, alight source of the above-described excitation light and alight source of the above-described probe light can be also made ofsemiconductor laser beam-emitting means of being output-controllable.

In such a construction, since it is possible to perform the outputcontrol which is a characteristic of the semiconductor laserbeam-emitting means, stable measurement with few noise is attained. Inaddition, a gas laser usually requires about 10 minutes from start-up tothe stabilization of temperature, and in consequence, the stabilizationof an output, and tends to be influenced by a change in externaltemperature. However, in the photothermal spectroscopic analyzer havingsuch construction as described above, it is possible to have one minuteor less of start-up time by controlling an output directly even if atemperature change happens, and it is hard to be influenced by a changein external temperature.

Furthermore, in the photothermal spectroscopic analyzer of the presentinvention, it is preferable to set the wavelength of the above-describedexcitation light at 400 to 700 nm.

In such a construction, it is possible to decrease background noise,caused by water absorption generated because near-infrared light withthe wavelength of about 780 nm is used for excitation light up to now,by approximately one figure, and hence, it is possible to enhance theaccuracy of measurement.

Furthermore, in the photothermal spectroscopic analyzer of the presentinvention, alight source of the above-described excitation light can bealso made of semiconductor laser beam-emitting means where electricmodulation can be performed.

In such a construction, since mechanical modulation means such as achopper required in a conventional gas laser become unnecessary,problems of generating physical vibration, upsizing an optical system,and increasing apparatus cost, which are caused by installing mechanicalmodulation means never arise.

Furthermore, the photothermal spectroscopic analyzer of the presentinvention may be also equipped with signal extraction means bysynchronous detection.

In such construction, since it becomes possible by using theabove-described electric modulation to perform highly precise signalextraction with a lock-in amplifier etc., it is possible to enhance theaccuracy of measurement.

Furthermore, the photothermal spectroscopic analyzer of the presentinvention may be also equipped with means of adjusting the distancebetween at least anyone of focal points of the above-describedexcitation light and the above-described probe light, and theabove-described sample cell which contains the above-described sample byusing the light reflected from the above-described sample cell.

In such a construction, since it is possible to quantify the positionalrelation of the focal points of excitation light and probe light, and asample cell by using the light reflected from the sample cell, itbecomes possible to perform the highly precise adjustment of a locationwhich is needed when a condenser lens with large numerical aperture isused. In addition, since the above-described positional relation can bequantified, it is possible to automate the adjustment of a location of asample cell after installing the sample cell in the photothermalspectroscopic analyzer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram showing a embodiment of a photothermalspectroscopic analyzer of the present invention;

FIG. 2 is a structural diagram explaining a construction of thephotothermal spectroscopic analyzer according to the example 1;

FIG. 3 is a chart showing a measurement result of a thermal lens signalin a xylene cyanol aqueous solution;

FIG. 4 is a graph showing a concentration dependency of a amplitude of athermal lens signal on the xylene cyanol concentration in a xylenecyanol aqueous solution;

FIG. 5 is a structural diagram explaining a construction of aphotothermal spectroscopic analyzer according to the example 2;

FIG. 6 is a chart showing an operation result of outputs of quadrantphotodiode at the time of moving a location of a sample cell; and

FIG. 7 is a structural diagram explaining a construction of aconventional photothermal spectroscopic analyzer.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of a photothermal spectroscopic analyzer according to thepresent invention will be described in detail with referring todrawings.

FIG. 1 is a structural diagram explaining the construction of aphotothermal spectroscopic analyzer according to an embodiment. Inaddition, this embodiment shows an example of the present invention, andthe present invention is not limited to this embodiment.

The photothermal spectroscopic analyzer in FIG. 1 comprises:semiconductor laser beam-emitting means 10 which is a light source ofexcitation light; semiconductor laser beam-emitting means 20 which is alight source of probe light; a sample cell 16 where a sample isinstalled; a focusing optical system which consists of collimator lenses11 and 21 for the above-described excitation light and theabove-described probe light, a condenser lens 15 which focuses theabove-described excitation light in the above-described sample andfocuses the above-described probe light to a thermal lens, and the like;a light-receiving optical system which consists of a filter 19 and apinhole 17, and detection means 18 which detects a degree of divergenceor convergence of the above-described probe light caused by theabove-described thermal lens.

In such a photothermal spectroscopic analyzer, excitation light isoutputted from the semiconductor laser beam-emitting means 10, and it isconverted into approximately collimated light by the collimator lens 11for excitation light. Then, after passing a prism 12 and a cylindricallens 13 (astigmatism correction means) which corrects astigmatism, it isfocused in the above-described sample, which is installed in the samplecell 16, by the condenser lens 15, and a thermal lens which is not shownis formed in the above-described sample.

In addition, probe light outputted from the semiconductor laserbeam-emitting means 20 is converted into approximately collimated lightby the collimator lens 21 for probe light. Then, it passes a prism 22,is made coaxial with the above-described excitation light by a beamsplitter 14, and is focused in the above-described thermal lens by thecondenser lens 15. The above-described probe light which is incident onthe above-described thermal lens formed in the above-described sample isgiven a thermal lens effect within the sample cell 16, passes a filter19 and a pinhole 17, is received by the detection means 18, and is givensignal analysis.

In addition, as the semiconductor laser beam-emitting means 10 and 20,semiconductor laser beam-emitting apparatuses or the like are used, anda photodiode or the like is usually used as the detection means 18.

Then, in this photothermal spectroscopic analyzer, since the collimatorlens 21 for probe light can be displaced in the direction of an opticalaxis of the probe light, the distance between the semiconductor laserbeam-emitting means 20 and the collimator lens 21 for probe light can bechanged. When the above-described distance is changed by displacing thecollimator lens 21 for probe light, a focal point of the probe light isdisplaced, and hence, the collimator lens 21 for probe light isdisplaced so that the probe light may focus in the most preferablelocation (location where measurement can be performed in highsensitivity) in the above-described thermal lens, and thereafter, thecollimator lens 21 for probe light is fixed.

In addition, the above-described distance may be changed by displacingthe semiconductor laser beam-emitting means 20 instead of the collimatorlens 21 for probe light, or the above-described distance may be changedby displacing both.

Furthermore, similarly, also in the excitation light, a focal point ofthe excitation light may be made controllable to a focal point of theprobe light by making at least any one of the semiconductor laserbeam-emitting means 10 and the collimator lens 11 for excitation lightdisplaceable.

Hereafter, each part of the photothermal spectroscopic analyzer in FIG.1 will be individually described.

(With Respect to Semiconductor Laser)

Although the wavelength of a semiconductor laser used as excitationlight is acceptable so long as it is within a range where a sample has acertain amount of absorption, it is desirable that it coincides with themaximum absorption wavelength of the sample.

However, it is known that, when an analysis of an aqueous solution isperformed by using light with the wavelength of about 780 nm asexcitation light like the conventional, in this wavelength region, abackground signal that originates in water absorption and cannot bedisregarded arises, and hence the accuracy of measurement falls.Therefore, as for the wavelength region of the excitation light, it isdesirable to use a visible light region of 400 to 700 nm.

In addition, as for an output of the semiconductor laser, sincemeasurement sensitivity improves in proportion to the output, it isdesirable that it is as high as possible. Therefore, what is necessaryis just to select wavelength to which an absorbance becomes as high aspossible in consideration of a molar extinction coefficient of water, amolar extinction coefficient of a measuring object, and an output of asemiconductor laser.

In addition, generally, a semiconductor laser is classified into anindex guided type or a gain guided type. An index guided typesemiconductor laser has characteristics such as a single spectrum incomparison with a gain guided type, usually small output variation, andastigmatism of 10 μm or less. In application to a thermal lensspectrometry, since the above-described three characteristics influencean S/N ratio (Signal-to-Noise ratio) of a thermal lens signal, it isdesirable to use an index guided type.

On the other hand, as for a semiconductor laser used as probe light,what is necessary is that wavelength differs from the wavelength of theexcitation light, and an output is acceptable so long as the detectionmeans 18 to be used can fully detect it. However, as for wavelength, itis more desirable that absorption by the measuring object is small andabsorption by other impurities is small. In addition, when a sample hasphotolysis property, it is desirable to use a semiconductor laser withthe wavelength nearer to a infrared region. As for a waveguide type, anindex guided type semiconductor laser is desirable like the case of theexcitation light.

In addition, as another types of semiconductor lasers, since adistributed feed back (DFB) type and a distributed Bragg reflector (DBR)type which are made by engraving a diffraction grating in each resonatorcan narrow spectral band width and can stabilize wavelength, they aredesirable.

Furthermore, as semiconductor lasers which can be used, it is possibleto use a laser where beam geometry of outgoing light is made to be aperfect circle by incorporating an optical system for the formation of aperfect circle (for example, a micro lens) into a semiconductor laserdevice itself although outgoing light is still divergent light, or it isalso good to use outgoing light from an optical fiber by connecting theoptical fiber to a semiconductor laser. In these cases, although itbecomes unnecessary to separately provide means for forming a perfectcircle, it still be very effective means to bring outgoing light closeto collimated light by using a collimator lens, and to adjust a focalpoint by a condenser lens since the outgoing light is divergent light.

Similarly, since there is a light emitting diode (LED) as small andinexpensive light-emitting means, it is also good to use an LED equippedwith the required output instead of a semiconductor laser. Furthermore,if outgoing light from LED is separated into spectrum by certain means,it is possible to narrow spectrum just like a semiconductor laser, andif the wavelength to be separated into the spectrum is changed, itbecomes possible to obtain the absorption spectrum of a measuring objectwithin the range of the oscillation wavelength of the LED, which becomesmore desirable.

In addition, although being expensive, a small solid state laser (forexample, YAG laser etc.) can be used for either the excitation light orthe probe light.

As a mechanism driving the semiconductor laser, any one of an outputcontrol type or a current control type is acceptable. However, since theoutput control type does not need the Peltier element described later,total cost is reduced by its part cost.

In the output control type, since it acts as a direct monitor of anoutput from a semiconductor laser to regulate its signal level, theoutput does not change even if a temperature change happens by laseroscillation, and hence, the influence on a measurement becomes small.This is because the output of the semiconductor laser can be controlleddirectly by a drive voltage, and, unlike a gas laser, its stability canbe made to 1% or less.

Owing to such characteristics, a semiconductor laser can obtain 1% orless of output stability within 1 minute after start-up. In addition,similarly, also in an on-site analysis, although it is easily expectedthat a temperature change by the convection of air etc. happens, anoutput can be kept constant also in that case, and hence, outputcontrollability is also a very important characteristic in POC analysisetc.

In the current control type, although a drive current is set constant,its output is influenced by a temperature change. In this case, theoutput can be stabilized if the temperature of the semiconductor laserbeam-emitting apparatus is lowered by a Peltier element etc. to keepconstant temperature. Furthermore, it becomes possible to prolong thelife of a semiconductor laser and a frequency of apparatus maintenancemay be fewer, which is desirable. Furthermore, the fluctuation of thesemiconductor laser beam in the axial direction by a temperature changeinside a resonator can be reduced and the noise in the above-describeddetection means 18 can be reduced by such temperature control, whichbecomes still more desirable.

It is preferable that an electric modulation mechanism is provided in anexcitation light controller for excitation light to be able to bemodulated electrically. Thus, if the output of the excitation light canbe modulated according to the electric modulation mechanism, thisbecomes a periodic repeat signal, and hence it becomes possible toperform integrationetc. in signal extraction, and the above-describedS/N ratio can be improved. In addition, since this enables the use ofsynchronous detection means such as a lock-in amplifier for signalextraction, the further highly accuracy is realizable.

Furthermore, if this modulation is enabled to about 100 MHz, amodulation frequency for a thermal lens is usually about 10 kHz in themaximum and frequency bands differ 10000 times, and hence, it becomepossible to superimpose two frequency simultaneously without beinginfluenced by this high frequency. Therefore, while thermal lensmeasurement is attained, the increase of noise by return light isreduced.

In addition, since a rare gas laser such as He—Ne laser cannot performelectric modulation, it is necessary to newly provide mechanicalmodulation means such as a chopper into an optical path of theexcitation light. In this case, since vibration originating in therotation of the chopper arises and it becomes noise, it may become afactor which further disturbs the miniaturization of an apparatus, andcost reduction.

(With Respect to Focusing Optical System)

As mentioned above, in a thermal lens spectrometry, focusing excitationlight to an optimal range, and making a focal point of probe lightdiffer from a focal point of excitation light are important points forrealizing a high S/N ratio.

The outgoing light of a semiconductor laser is divergent light, and itsdivergence angle is different according to the cross sectional directionof abeam. Furthermore, since there is astigmatism that a focal pointdiffers according to the cross-sectional direction of a beam even if theabove-described outgoing light is focused by a lens, it is necessary tocorrect it when being incident on a thermal lens. Since it becomespossible by this correction to uniquely specify beam diameter and afocal point without depending on cross-sectional geometry, this isdesirable because of easy optimization of the beam diameter and focalpoint. In addition, even if a beam just after out-going fromsemiconductor laser beam-emitting means is focused in a sample with alens as it is, focusing to the beam diameter of 10 μm or less isimpossible.

Then, it is desirable to collimate excitation light by the collimatorlens 11 for excitation light. Owing to this, the outgoing light that isdivergent light is collimated to be made collimated light. As for thecollimator lens 11 for excitation light, a single lens may be used, or acombination lens is sufficient so long as it has positive focal length,or a GRIN lens with refractive index distribution maybe used.Preferably, it is desirable to use the combination lens whose aberrationis corrected since it can suppress the aberration to the minimum and cankeep beam characteristics good. In addition, it is still more desirablethat the aberration generated by the thickness of an outgoing window ofa semiconductor laser is corrected. As for these lens characteristics,the collimator lens 21 for probe light is the same.

In addition, since semiconductor laser beam-emitting means is weak inreturn light by an optical system and a noise component becomes largesince output variation etc. are produced by return light, it isdesirable that both the collimator lenses 11 and 21 are givenantireflection coating etc.

As mentioned above, when sharing a condenser lens between the excitationlight and the probe light for making beam diameter small to some extentand focusing the beam to a sample, the simple adjustment means of afocal point of the probe light is to displace the collimator lens 21 forprobe light from its collimate location to the direction of an opticalaxis.

In a conventional method, a focal point of the probe light was adjustedat a point where sensitivity becomes optimum by displacing a lenslocation in the direction of an optical axis by using separate condenserlenses for excitation light and probe light. However, in this case,since it is not possible to secure a space for making the excitationlight and probe light coaxial when the focal length of each condenserlens is shortened in order to improve focusing property, there is alimitation in making the beam diameter in a focal point small.

In this embodiment, it is possible to realize the small beam diameter ofthe excitation light and the simple adjustment of a focal point of theprobe light simultaneously with fewest number of parts. This becomespossible because the outgoing light of the semiconductor laser isdivergent unlike a gas laser.

Thus, when the gas laser which is collimated light is used, a focalpoint cannot be adjusted even if the distance in the direction of anoptical axis between the light source of the probe light, and thecollimator lens 21 for probe light is changed. In addition, thecollimator lens 21 for probe light can adjust a focal point of probelight, and can bring the outgoing light of a semiconductor laser closeto collimated light and lead it to a condenser lens in optimal beamdiameter, it becomes possible to simultaneously realize two importantfunctions of increasing a degree of focusing of probe light andsuppressing power loss, in the thermal lens spectrometry.

It is desirable to use a lens with longer focal length for thecollimator lens 21 for probe light which most simply adjusts a focalpoint like this embodiment. If a lens with especially short focal lengthis used, it becomes possible to use large numerical aperture, and canbring a beam close to collimated light with suppressing the power lossin the collimator lens 21 for probe light to the minimum. However, inusing a semiconductor laser as probe light, a collimated beam becomes anellipse determined by a ratio of divergent angles in the cross sectionaldirections, and if it is focused while it is elliptic, the beam waist ina focal plane, i.e., a focus takes on different values according as thecross sectional direction.

The optimal difference of focal point of excitation light and probelight which are known in well-known technology depends on this beamwaist (Thierry Berthoud et al., Anal. Chem., Vol. 57, 1216–1219, 1985).However, about the optimal value, since it is dependent on various otherparameters and is complicated, each theoretical formula proposed up tonow is not perfect, and hence, forecast is impossible. Therefore, it isnecessary to determine an optimal value experimentally according to asystem.

Since the optimal difference of the focal points differs when the beamwaist changes according to the cross sectional direction as describedabove, it is difficult to set an optimal value for both directions. Inthis case, it is necessary to correct the collimated beam, which iselliptic, by providing the means, which enlarges the beam in only onedirection, such as a prism, immediately after a collimator lens. Inaddition, the optimal difference of focal points changes also with thevalue of the astigmatism of a semiconductor laser.

When a focal length is long to some extent, a stray arises in thecollimator lens 21 for probe light, and it causes power loss. However,since its outgoing light has a profile near a perfect circle rather thanan ellipse and a degree that a value of beam waist also differsaccording to the cross sectional direction becomes small, it becomeseasy to set the difference of focal points optimal. Also in this case, asimplest and low-cost method as means of adjusting a focal point is todisplace the collimator lens for probe light in the direction of anoptical axis from a collimating location.

In this embodiment, although a common condenser lens 15 for focusing isinstalled unlike conventional technology in order to focus a beam and toimprove sensitivity, it is possible to adjust a focal point simply andcontinuously according to necessity, by displacing the location of thecollimator lens 21 for probe light in this case. Since it is notnecessary to change in particular the characteristics of a lens evenwhen a divergent angle varies with the lot of a light-emitting apparatuslike a semiconductor laser, this is very effective. In addition, whenastigmatism is very large like a gain guided type semiconductor laser,an optical system (cylindrical lens etc.) which corrects the astigmatismmay be provided in front of or behind this collimator lens 21.

Next, when optical path length is further short like an analysis inμ-TAS, an optical system for making a beam of excitation light smalleris further needed.

First, since the sensitivity of a thermal lens signal is proportional tothe intensity of excitation light, it is necessary to design an opticalsystem so that power loss may be suppressed as much as possible.Therefore, the collimator lens 11 for excitation light with much longfocal length cannot use. In addition, if it is shortened too much, anincident angle to the prism 12 which enlarges a beam in only onedirection become large and reflection loss at the place becomes largenonlinearly at Brewster's angle or more as derived from a Fresnelequations, and hence, it is necessary to determine a focal length inconsideration of this reflection loss and loss by the stray at thecollimator lens 11 for excitation light.

In particular, these losses become more remarkable when the major axisof an ellipse and the polarization direction of a semiconductor laserbeam in a far-field (point which is separated from an exit aperture of asemiconductor laser by 50 cm or more) of the outgoing light of asemiconductor laser coincide. In this case, when two prisms 12 areprepared and are used as a prism with facing each other for inclinedfaces, it is possible to lessen an incident angle to each prism 12 withfixing a magnification, and hence, it is desirable since the power lossof the excitation light by reflection loss can be suppressed. Theincident angle to the prism 12 may be set at an angle at which the majoraxis and minor axis of an ellipse determined by the focal length of thecollimator lens 11 for excitation light become equal to each other.

The beam splitter 14 is required in order to lead the excitation lightand probe light to the condenser lens 15 coaxially, and it is desirablethat its reflectance for excitation light is close to 100%. In addition,it is desirable that a transmittance ratio for probe light is atransmittance ratio at which required sensitivity can be obtained in thedetection means 18.

In addition, as for the condenser lens 15, it is desirable for lesseningpower loss that its pupil diameter is nearly equal to the beam diameterof the excitation light just before incidence. As for the condenser lens15, although it can be made of a lens which consists of a single lens ortwo or more lenses, it is desirable that it is an aberration correctinglens.

In addition, a cylindrical lens 13 is used as correction means when theastigmatism of excitation light is large, and is installed immediatelyafter the prism 12. Furthermore, it can be installed after thecollimator lens 11 for excitation light.

Such an optical system for tightly focusing a beam smaller enables theenhancement of alignment accuracy when performing the alignmentautomatically by using the light reflected from the sample cell 16 whichconsists of glass, a resin, or the like, and is effective formeasurement automation.

(With Respect to Light-receiving Optical System)

Light-receiving optical system has rolls of cutting the excitation lighttransmitting or being reflected from a sample, and leading the center ofthe probe light similarly transmitting or being reflected from thesample to the detection means 18. In addition, this embodiment is thecase where the transmitted light is used.

In this embodiment, although a filter 19 is used for the cut of theexcitation light, a spectrometer or the like can be used. In addition,since the filter 19 with higher optical density is better, it isdesirable that it is five or more.

In addition, although a pinhole 17 is adopted as an article of makingonly a core part of the probe light, transmitting or being reflected,transmit, it is also good to lead only the center part of the probelight to the detection means 18 without using the pinhole 17.

Up to now, the necessary distance from the sample 16 to the pinhole 17is usually about 1 m. Namely, if the pinhole 17 is not installed in alocation which is apart by 1 m or more from a thermal lens which is notshown but exists in the sample 16, a change in light intensity of theprobe light by a thermal lens effect becomes small, and in consequence,the sensitivity of a thermal lens signal falls.

This becomes an obstacle for the miniaturization of the whole opticalsystem including the light-receiving optical system. In addition, if anoptical path is lengthened as described above, pointing noise by thefluctuation of laser light in the direction of an optical axis becomelarge, and hence, this become a cause of lowering the S/N ofmeasurement.

In this embodiment, since the focusing degree of a condenser lens isincreased for the improvement of sensitivity and a degree of focusing ofprobe light is also improved in connection with it, it is possible toshorten the distance from a sample to a pinhole.

The beam diameter of probe light in conventional technology was about200 μm at the minimum, and the necessary distance from a sample to apinhole was at least about 1 m. However, in this embodiment, as shown inthe following example, when the beam diameter of the probe light was 9μm, the distance from the sample to the pinhole was 2 cm, and thesensitivity of an absorbance was higher by one figure than that inconventional technology.

Therefore, it can be seen that, when the beam diameter increases toabout 20 times, the distance from the sample to the pinhole becomes 50times. If this distance is allowed to be up to 10 cm, what is necessaryis to perform proportion simply and to make the beam diameter of theprobe light up to about 50 μm. In addition, in order to shorten theabove-described distance more than this, what is necessary is just tofurther focus the probe light, and it can be made to 0.2 μmtheoretically.

In this embodiment, since an optical system including a light-receivingoptical system is integrated into a unit by using a semiconductor laserand simple focal point adjustment means for probe light is alsoprovided, what limits its size is the size of component parts themselvesin the optical system from a light source to a condenser lens, andhence, shortening the distance between a sample and a pinhole leads tothe miniaturization of the optical system as it is.

Although the above is the case where detection is performed by using thetransmitted light from a sample, it is also possible to shorten thedistance from a sample to a pinhole in the case of using the reflectedlight from the sample, similarly. In case of using the reflected light,what is necessary is just to attach a certain reflective film to thesample cell 16, or to provide a mirror after the sample cell 16. In caseof directly attaching a reflective film to the sample cell 16, theintensity of the reflected light from this film becomes large asdescribed later. Therefore, by using this reflected light, this isdesirable since it becomes easy to perform optical auto-focusing asdescribed later. However, in the case that this reflective film absorbsthe above-described excitation light with exceeding 1%, a true signal isaffected by this as a background signal, and hence, it is desirable touse a low absorptive material with 1% or less of absorptance.

In addition, since it is likely to cancel a thermal lens effect beforeand after reflection if a focal point of the probe light is further froma condenser lens 15 than a focal point of the excitation light whenusing the reflected light, it is desirable that the focal point of theprobe light is closer to the condenser lens 15 than the focal point ofthe excitation light.

A photodiode or the like which has sensitivity to the wavelength of theprobe light is used as the detection means 18. If necessary, it is alsogood to provide an amplifier with low noise in the detection means 18,and, to finally amplify an electric signal to required amplitude.

(With Respect to Sample Cell and Sample)

As for the sample cell 16 for installing a sample, it is fundamentallyno problem that its cross sectional geometry is any geometry. It isdesirable that a surface into which a light comes and through which thelight is transmitted may be flat. Other faces may have rectangularcross-sections whose depth (optical path length) only is shallow butwhose width is wide, or a thin glass capillary with 10 μm to hundreds μmof width, a micro channel made by processing a microchip with ultra-fineprocessing technology, or the like is also sufficient. In addition, itis desirable that the depth of a sample cell is 1000 μm or less so thatthe amount of a used solution may become minimum.

In addition, although it is possible to use it without a specificproblem so long as it is optically transparent material as the materialof the sample cell 16, it is desirable to use a low absorptive materialwith 1% or less of absorptance since a true signal is affected by it asa background signal when absorbing the excitation light by exceeding 1%.For example, transparent resins such as an acrylic resin, apolycarbonate resin, and a polystyrene resin are cited. It is possibleto produce a microchannel etc. by injection molding, compressionmolding, etc. by using these resins.

A sample which is a measuring object is not especially limited so longas it absorbs the wavelength (for example, 635 nm) of the excitationlight. So long as a signal processing method for extracting a componenthaving the same period as a modulation frequency of the excitation lightsuch as a lock-in amplifier detection is adopted even if the wavelength(for example, 780 nm) of the probe light is absorbed, the influencewhich the absorption of the probe light by the sample gives to a thermallens signal is small.

In particular, in case of applying a semiconductor laser to a doublebeam method like this embodiment, a mechanical modulation mechanismwhich needs processing and rotation accuracy is unnecessary, and hence,it is possible to inexpensively modulate the excitation light by acurrent. Usually, since the overshoot and vibration which originate inthe relaxation oscillation of excitation electrons in a resonator of thesemiconductor laser at a leading edge or a trailing edge of its waveformare observed if the excitation light is modulated, remarkable influenceis given to a thermal lens signal since the change of this waveform isadded to a waveform change by a thermal lens effect in the case of asingle beam method of detecting the excitation light as it is.

However, in the case of the double beam method like this embodiment, inaddition to the detection of the probe light, instead of the excitationlight which is modulation light, the time of the above-describedrelaxation oscillation is dozens ns, which is very short in comparisonwith several ms to hundreds ms of leading time constant of the thermallens and is negligible, and hence, the modulation of the excitationlight can become inexpensive and simple modulation means with hardlyaffecting the thermal lens signal.

On the other hand, when the sample consists of many components andsubstances except objective substance absorb the wavelength of theexcitation light, it is difficult to extract a thermal lens signal thatis unique to the objective substances. However, also in this case, asshown in measurement in impurities such as a blood test, if only theobjective substance can be made to uniquely color by using an enzymereaction, it is satisfactory. As such an example, there is a reactionsystem of the enzyme reaction or coloring of cholesterol measurement inblood, and it is possible to quantitatively measure the concentration ofcholesterol by the thermal lens spectrometry by using a kit such ascholesterol E-HA test Wako (made by Wako Pure Chemical Industries, Ltd.)or the like.

In addition, since plenty of reaction systems which specifically reactonly to objective substances by enzyme reactions or complex formingreactions besides this example, and make them finally color are known,it is possible to perform measurement in blood or environmental water,where many impurities exist, or the like in sufficient accuracy by usingthese.

(With Respect to Alignment Procedure)

Up to now, a microscope has been used for alignment when a degree offocusing of a condenser lens has been improved. That is, a location of asample cell was adjusted at an optimal location for measuring a thermallens signal by visually adjusting the positional relation of the samplecell and a focal point of a beam by using the microscope.

However, as for usual microscopes, since the size of even a small onewas 15 cm D×15 cm W×30 cm H, an optical system became large-sized, andthe adjustment of a location of the sample cell was manual adjustmentwith eyes, and hence this has become an obstacle in realization of highaccuracy and automation of a photothermal spectroscopic analyzer.

In this embodiment, since a location of a sample cell is opticallydetected and is quantified by using the reflected light from the samplecell, a microscope became entirely unnecessary and sharp improvement isperformed also in respect of miniaturization.

As the above-described optical detection method, it is possible to cite,for example, an astigmatic method of dividing light, reflected from asample cell, by a beam splitter, further letting it pass through acylindrical lens, recognizing the cross sectional geometry of theabove-described reflected light with a quadrant photodiode, anddetermining the positional relation of a sample cell and a focal point.Although such an astigmatic method is desirable since the sensitivity ofdetection of a focal point is high, a method of optically detecting alocation of a sample cell is not limited to the astigmatic method, but acritical angle method or a knife edge method is also sufficient ifsensitivity required is obtained.

Since it is possible to highly accurately detect a boundary betweenglass and air and a boundary between glass and a sample when a glasssample cell is used by using such a focus servo, it is possible to aligna focal point with an arbitrary point with high accuracy by utilizingthe result and using a stage etc.

In particular, in this embodiment, since it is possible to share acondenser lens between the excitation light and probe light and togreatly make a beam small, it becomes possible to perform alignment withprecision equivalent to a micrometer became possible by theabove-described focus servo.

In addition, as described above, when using a reflective optical systemfor a light-receiving optical system, it is possible to share thelight-receiving optical system and autofocus optical system by detectinga change in a focal point by the thermal lens effect by using not only adetection method with a pinhole but also the above-described servo whichdetermines a focus position, and hence, it is also possible to obtain asimplified optical system.

In addition, since the excitation light has short wavelength and isincident on an objective lens in cllimated light if the excitation lightis used for such an alignment, beam diameter in a focal point becomessmall, and hence, alignment with high accuracy becomes possible. Inaddition, it is possible to adjust a focal point highly accurately andautomatically also in the direction of groove width by using the samemethod when it is necessary to align a focal point in a thin groove in amicrochip etc. and only changing a computing method of each quantity oflight detected by a quadrant photodiode.

Next, the measurement using a photothermal spectroscopic analyzeraccording to the present invention will be described in detail withreferring to drawings.

EXAMPLE 1

An example where optics are separately fixed on an optical bench, amicroscope is used, and both the light sources of excitation light andprobe light are made of semiconductor laser beam-emitting apparatuseswill be described in detail.

FIG. 2 is a structural diagram explaining a construction of aphotothermal spectroscopic analyzer used in this example. In addition,since the construction of a photothermal spectroscopic analyzer in FIG.2 is almost the same as the construction of the photothermalspectroscopic analyzer in FIG. 1, only different portions will bedescribed and the explanation of the same portions will be omitted. Inaddition, in FIG. 2, the same symbols in FIG. 1 are assigned to theportions identical or equivalent to those in FIG. 1.

A semiconductor laser beam-emitting apparatus with the wavelength of 635nm and a rated output of 20 mW (DL-4038-025 made by SANYO Electric Co.,Ltd.) was used for a light source 10 of excitation light. A constantcurrent control driver (TC-05 visible light type DPST2001, Japan ScienceEngineering Co., Ltd.) equipped with a Peltier element which can performtemperature control of a semiconductor laser device at about 25° C. wasused in a drive circuit of this apparatus. In addition, since thisdriver is equipped with a modulation function, it is possible tomodulate an output at an arbitrary frequency by inputting a modulationsignal from the external device. A function generator (8116A, made byHewlett-Packard Co.) was used for such a modulation signal generator.

In addition, a semiconductor laser beam-emitting apparatus with thewavelength of 780 nm and a rated output of 15 mW (DL-4034-151, SANYOElectric Co., Ltd. make) was used for the light source 20 of probelight. A constant current control driver (TC-05 infra-red type DPST2001,made by Japan Science Engineering Co., Ltd.) equipped with a peltierelement which can perform temperature control of a semiconductor laserdevice at about 25° C. was used in a drive circuit of this apparatus.

Furthermore, a collimating lens for a laser diode with the focal lengthf of 14.5 mm and the numerical aperture of 0.276 (06GLC003, made byMelles Griot Inc.) was used for the collimator lens 11 for excitationlight. Then, the same lens as is described above was also used for thecollimator lens 21 for probe light. Translation stages (07TAC504, madeby Melles Griot Inc.) which are not shown were provided in mounts ofboth of these collimator lenses 11 and 21 to make it possible todisplace them in the resolution equivalent to a micro meter in thedirection of an optical axis.

Furthermore, no-mount prisms for a pair of anamorphic prisms (06GPU001,made by Melles Griot Inc.) were used for the prism 12 for excitationlight and the prism 22 for probe light.

Moreover, a wavelength dependent beam splitter for a laser diode(03BDL003, made by Melles Griot Inc.) was used for the beam splitter 14.Since having a reflective band of 550 to 650 nm, and a transparency bandof 760 to 1600 nm, this can reflect or transmit the excitation light(635 nm) and probe light (780 nm), which were used for the photothermalspectroscopic analyzer of this example, by about 100%.

Furthermore, a tool microscope equipped with the half mirror 31 (XR1004,made by Carton Optical Industries, Ltd.) was used for the microscope 30so that the excitation light and probe light which were made coaxialcould be introduced from its side. In addition, an antireflectioncoating that acts at 635 nm and 780 nm is applied to the half mirror 31.An achromat objective lens with the numerical aperture of 0.4 (M955-40,made by Carton Optical Industries, Ltd.) was used for the objective lens32 of the microscope 30. This objective lens 32 plays the role of acondenser lens (condenser lens 15 in FIG. 1) which focuses excitationlight in a sample and focuses probe light in the above-described thermallens. In addition, a similar lens was used for the objective lens 33 forlight-receiving.

Furthermore, a laser line interference filter (03FILO56, made by MellesGriot Inc.) with the central wavelength of 780 nm and the half width of20 nm was used for the filter 19 which cuts the excitation light.

Moreover, a silicon PIN photodiode (DET110, made by THORLABS Inc.) wasused for the detection means 18. An output from this detection means 18is a voltage output by a 50-Ω terminator (T4119, made by THORLABS Inc.)which is not shown. A low noise preamplifier with the gain of 100(LI-75A, made by NF Circuit Block Corporation) was used for voltageamplification (not shown). Then, a two-phase lock-in amplifier (5610,made by NF Circuit Block Corporation) was used for a thermal lens signaldetector (not shown).

An output of this lock-in amplifier was connected to a connector(CB-50LP, made by National Instruments Corporation) through a BNC cable,and an output from the connector was fetched into a notebook computerwith a data acquisition card (DAQCARD-700, made by National InstrumentsCorporation). A signal fetched into the notebook computer was displayedon a display unit of the above-described notebook computer by software(Labview 5.0, made by National Instruments Corporation), and was savedin a recording device of the above-described notebook computer. Inaddition, in order to measure the beam diameter, coordinates of acenter, an inclination angle of a major axis of an ellipse, an output,and those time-dependent changes of a laser beam, a beam analyzer (BeamAlyzer 13SKP001-SA, made by Melles Griot Inc.) which was not shown wasused.

Furthermore, an automatic positioning stage (MINI-60X MINI-5P, made bySIGMA KOKI CO., LTD.) which can position two axes in the direction of anoptical axis and the direction perpendicular to the optical axis in a1-micrometer level of resolution was used for the stage 34 on which thesample cell 16 was placed.

Next, methods from the adjustment of an optical system to measurement ofa thermal lens signal in the above-described photothermal spectroscopicanalyzer will be described.

At the time of adjusting the optical system, first of all, the probelight is adjusted. With looking at the analysis result of the beam bythe above-described beam analyzer, the light source 20 of the probelight is mounted so that the major axis of an ellipse of outgoing lightmay become perpendicular to the top face of a surface plate on which theoptical system is fixed. Next, the optical axis of the collimator lens21 for probe light is adjusted. Thus, beam diameter in a point near thecollimator lens 21 for probe light and a point apart by about 1 m ismeasured with the above-described beam analyzer, distance between thelight source 20 of the probe light and the collimator lens 21 for probelight is adjusted so that they may become equal, and the location isdetermined to become collimated light (reference location). Thecollimator lens 21 for probe light was adjusted at a location whichbecomes optimal for thermal lens measurement by displacing thecollimator lens 21 for probe light from the reference location by fixeddistance. The focal point of the probe light is uniquely determined bythe amount of displacement from the reference location.

Next, the prism 22 is installed as shown in FIG. 2, and is rotated on arotation stage etc. until the minor axis of an ellipse of theabove-described outgoing light becomes coaxial with the major axis, andan incident angle is adjusted. After letting the outgoing light fromprism 22 pass through the beam splitter 14, the microscope 30 isinstalled and the probe light is incident on the objective lens 32 ofthe microscope 30. Furthermore, in order to receive the transmittedlight from the sample which was placed in the sample cell 16, theobjective lens 33 for light-receiving is installed, an axis of thisobjective lens 33 is aligned with the optical axis, and it is adjustedso that the outgoing light may become collimated light.

Then, the filter 19 is arranged between the objective lens 33 forlight-receiving, and the detection means 18. In addition, although apinhole could be established between the filter 19 and detection means18 as shown in FIG. 1, in this example, the pinhole was substituted byshifting the objective lens 33 for light-receiving from a location,where collimated light was obtained, in the direction of the opticalaxis to make it stray in the condenser lens 33. At this time, thedistance between the sample cell 16 and the objective lens 33 that wasan alternative of the pinhole was about 2 cm.

After the adjustment of the probe light finishes, the installation ofthe light source 10 of the excitation light and the adjustment of thecollimator lens 11 for excitation light and the prism 12 are performedby the same method.

Then, the excitation light and probe light are made to be coaxial bysuch adjustment at two points that the optical axis of the excitationand probe light is aligned on the beam splitter 14, and optical axes ofboth light are aligned at a location distant enough from the beamsplitter 14 after adjusting the swing and tilt of the beam splitter 14.When axes coincide at two points, the excitation light is alsoperpendicularly incident on a pupil of the objective lens 32. It is goodto install a swing and tilt mirror in a suitable place to make the aboveadjustment still easier. In addition, the optical path length from thelight source 10 of the excitation light and the light source 20 of theprobe light to the sample cell 16 is about 50 cm.

An analysis was performed by using such a photothermal spectroscopicanalyzer, using a glass cell (AB20, made by GL Sciences, Inc.) with theoptical path length of 50 μm as the sample cell 16, and using a xylenecyanol aqueous solution as the sample.

On the occasion of measurement, the sample cell 16 where the sample isinstalled first is put on the stage 34. Then, a location of the samplecell 16 is adjusted so that the excitation light and probe light may beincident on a measured portion. Furthermore, a focal point (depthlocation) of the excitation light is adjusted. In that time, it is goodto adjust the focal point by using a microscope etc., while displacingthe sample cell 16 by moving the stage 34. When the focal point exactlycoincides with a boundary between air and glass, or a boundary betweenglass and the sample, the sample cell 16 is displaced by using the stage34 on the basis of a bright spot since its reflected light is clearlyobserved as the bright spot under the microscope. In this way, afterpositioning the focal point at a predetermined depth location,measurement is performed by the thermal lens spectrometry.

FIG. 3 shows the result of measuring the time-dependent change of athermal lens signal in a xylene cyanol aqueous solution with theconcentration of 25 μM. Measurement was performed for 5 minutes atintervals of 1 second. The modulation frequency was set at 2.1 kHz andthe time constant of the lock-in amplifier was 1 sec. In addition, boththe beam diameters of the excitation light and probe light at this timewere about 9 μm.

As apparent from a chart in FIG. 3, although an output from the lock-inamplifier was 0.07 V on average when only the probe light was incident,and on the contrary, an output was about 6 V when the thermal lens wasmade to be formed by incidence of the excitation light. Since thestandard deviation σ of the measurement for these 5 minutes is 0.044 V,CV (Coefficient of Variance) of the measurement at this time is about0.7%, and hence, it can be seen that very stable measurement wasperformed.

FIG. 4 shows a correlation between the amplitude of a thermal lenssignal and the xylene cyanol concentration in the measurement of athermal lens signal in a xylene cyanol aqueous solution. From thisresult, supposing detection limit concentration is the concentration atwhich S/N (Signal-to-Noise ratio) becomes 2, it was 3.6×10⁻⁷ (mol/L).When the detection limit of absorbance in the photothermal spectroscopicanalyzer of this example was found by multiplying it by a molarextinction coefficient of 3×10⁴ (L/cm/mol) and the optical path lengthof 5.0×10⁻³ (cm) of the xylene cyanol which were used in this example,it was about 5.4×10⁻⁵ (Abs.) in the aqueous solution.

Then, the detection limit of absorbance in the photothermalspectroscopic analyzer in FIG. 7 which is conventional technology was2×10⁻⁴ (Abs.), i.e., 0.2 ppb in the concentration of phosphorus, fromthe measurement where 2-butanol solution was used. However, since adetection limit is 0.7 ppb and a molar extinction coefficient inwavelength 823.9 nm becomes about ¾ times in comparison with the case ofthe 2-butanol solution when aqueous solution is used, the detectionlimit of absorbance in the aqueous solution is calculated to be 5.3×10⁻⁴(Abs.). Therefore, it can be seen that this example is ten times as highas conventional technology in sensitivity. In addition, in this example,the astigmatism was not completely corrected in both the excitationlight and probe light, but about 40 μm remains.

In addition, in comparison with another conventional technology that asemiconductor laser light source is adopted as the excitation lightsimilarly to the above, and the distance from a sample to a pinhole isshortened to 10 cm without contrivance (D. Rojas et al., Rev. Sci.Instrum., Vol.63, 2989–2993, 1992), this example is about 24 times ashigh as a conventional example in sensitivity (this conventional exampleis not shown).

As for the numerical aperture of a condenser lens, it is expected thatthere is a value at which sensitivity becomes optimal for the depth of asample cell as mentioned above. Namely, since the conventionaltechnology in FIG. 7 uses a sample cell with large depth that is 1 cm,it does not always lead to the enhancement of sensitivity to lessen thebeam diameter of the excitation light to smaller size than 70 μm.However, in this example, since a semiconductor laser was used, beamdiameters of the excitation light and probe light were set to 9 μm, anddistance from a sample to a pinhole was shortened to 2 cm, it becamepossible to measure the minimum amount of sample in the sample cell withthe depth of 50 μm with high sensitivity.

In addition, the adjustment of a focal point of the probe light isperformed by a simple method of increasing focusing degree by sharing acondenser lens, adjusting the distance between the light source 20 ofthe probe light and the collimator lens 21 for probe light by displacingthe collimator lens 21 for probe light without increasing a parts count.The measurement sensitivity is improved owing to this.

In addition, in this example, although both the distance between thelight source 20 of the probe light and the collimator lens 21 for probelight and the distance between the light source 10 of the excitationlight and the collimator lens 11 for excitation light were madeadjustable, it is also good to make one of them adjustable.

EXAMPLE 2

An example of which miniaturizing and integrating a portion from a lightsource to detection means will be described in detail with referring toFIG. 5. In addition, in FIG. 5, the same symbols in FIG. 1 are assignedto the portions identical or equivalent to those in FIG. 1. In addition,in this example, although several kinds of our own optics are used, itis natural to use commercial optics so long as they have the samecharacteristics.

A semiconductor laser beam-emitting apparatus with the wavelength of 635nm and a rated output of 30 mW (LTO51PS, made by Sharp Corporation) wasused for a light source 10 of excitation light. In addition, asemiconductor laser beam-emitting apparatus with the wavelength of 780nm and a rated output of 50 mW (ML60114R, made by Mitsubishi ElectricCorporation) was used for the light source 20 of probe light. Thesesemiconductor lasers were made to enable output control and currentcontrol by commercial LD drivers (ALP-6323CA, made by Asahi data systemsLtd.) which are not shown.

LD drivers are connected to a personal computer through a PCI card(NIPCI-6025E, made by National Instruments Corporation) which issimilarly not shown, and the personal computer can adjust the output,current, and modulation frequency of the semiconductor laserbeam-emitting apparatus. In addition, a modulation frequency of theexcitation light can be 0 to 100 kHz. Furthermore, both the excitationlight and the probe light superimposed 350 MHz of high frequencies tosuppress the influence by return light.

An own lens with the numerical aperture of 0.34 and the focal length of8 mm was used for the collimator lens 11 for excitation light. An ownlens with the numerical aperture of 0.39 and the focal length of 7 mmwas used for the collimator lens 21 for probe light. The collimator lens21 for probe light was attached on a micrometer head (MHT 3-5, made byMitutoyo Corporation) which is not shown, and was made to be able toperform displacement in the direction of an optical axis in a micrometerlevel of resolution. In addition, a displacement method is not limitedto this example.

Furthermore, an article made by making inclined planes of two own prismsface each other was used for the prism 12 for excitation light and theprism 22 for probe light. In addition, as for the prism 12 forexcitation light, an angle between two prisms was adjusted so that amagnification might become 3 times. In addition, as for the prism 22 forprobe light, an angle between two prisms was adjusted so that amagnification might become 2.6 times.

Furthermore, an own polarization dependent beam splitter whosetransmittance to p-polarized light was 100%, and whose reflectance tos-polarized light was 100% was used for the beam splitter 14 for makingthe excitation light and probe light coaxial. In addition, in this case,since the excitation light is s-polarized light and the probe light isp-polarized light, power loss in this beam splitter 14 is about 0.

Furthermore, the numerical aperture of 0.4 and the focal length of 4.5mm (350022, made by Geltech. Inc.) were selected for the condenser lens15.

In addition, in order to lead the excitation light and probe light,which passed the beam splitter 14, to the condenser lens 15, a mirrorprism 56 which makes both the above-described light refracted by 90° wasused.

Next, a method of quantifying the positional relation between the samplecell 16 and the focal point of a laser beam by using the reflected lightfrom the sample cell 16 will be described. In addition, in this example,although a method of quantifying the above-described positional relationby using an astigmatic method of detecting a location of the sample cell16 with the cross section geometry of a beam of the reflected light wasadopted, a method of quantifying the above-described positional relationis not especially limited, but a knife edge method or a critical anglemethod may be also used.

The reflected light from the sample cell 16 is led to an optical systemfor detecting a location of the sample cell 16 after being reflected byan own unpolarized light dependent beam splitter 51 whose transmittanceand reflectances to the excitation light and probe light are set at 80%and 20% respectively. Only the probe light out of the reflection lightof the excitation light and the probe light that are led to the opticalsystem is cut by a laser line interference filter 52 with the centralwavelength of 635 nm, and the half width of 10 nm (03FIL 250, made byMelles Griot Inc.), and is led to the condenser lens 53. An own lenswith the focal length of 45.5 mm was used for the condenser lens 53.

An own cylindrical lens whose focal length in a curved surface is 286 mmwas used for the cylindrical lens 54. The excitation light is focused bythe condenser lens 53 and cylindrical lens 54 at the quadrant photodiode55 (S6344, made by Hamamatsu Photonics K.K.), and light intensities infour photodiodes are converted into electric signals, respectively.These electric signals are led to a personal computer, which is notshown, through a PCI card (NIPCI-6025E, made by National InstrumentsCorporation) which is similarly not shown. Then, the relative distancebetween the sample cell and the focal point of the excitation light isquantified by performing data processing on the personal computer. Inaddition, in operation, the sum of outputs of two photodiodes located inopposing corners among four photodiodes of the quadrant photodiode 55was calculated, and the difference of the two operation values wasfurther calculated.

Next, an optical system of a light-receiving section will be described.In this example, although detection is performed by using thetransmitted light, it is also good to perform detection by utilizing thereflected light by using a mirror or a reflective film as mentionedabove.

In order to make into collimated light the excitation light and probelight which transmitted the sample, the same lens as the condenser lens15 was used for the light-receiving lens 57. In addition, the numericalaperture of the light-receiving lens 57 is satisfactory so long as it islarger than the numerical aperture of the condenser lens 15.Furthermore, a laser line interference filter with the centralwavelength of 780 nm and the half width of 20 nm (03FILO56, made byMelles Griot Inc.) was used for the filter 19 which cuts the excitationlight.

Only a center part of the probe light transmitted the filter 19 wastransmitted by the pinhole 17, was focused in the detection means 18 bythe lens 58 (01LPX005, made by Melles Griot Inc.) whose focal length is10 mm, and is converted into an electric signal. A quadrant photodiode(S6344, made by Hamamatsu Photonics K.K.) was used for the detectionmeans 18. In this example, the sum of each electric signal of fourphotodiodes was calculated, and its signal was made to be an output fromthe detection means 18. In addition, it is not necessary to use aquadrant photodiode for the detection means 18, but a non-splitphotodiode is also satisfactory.

The output from the quadrant photodiode was converted into a voltagefrom a current by an own circuit. A conversion scale factor from acurrent to a voltage was set at 1000 times. In addition, a commercialcircuit can be used as this conversion circuit from a current to avoltage so long as its conversion scale factor is 1000 times.

Furthermore, the converted voltage signal was led to a low noisepreamplifier with the gain of 100 (LI-75A, made by NF Corporation) (notshown), and is further led to two-phase lock-in amplifier (5610B, madeby NF Corporation) which is not shown. Then, only an electric signalwhich synchronizes with a modulation frequency of the excitation lightwas extracted, and it was made into thermal lens signal values (outputof the lock-in amplifier).

An output of this lock-in amplifier was connected to a connector(CB-50LP, made by National Instruments Corporation) through a BNC cable,and an output from the connector was fetched into a notebook computerwith a data acquisition card (DAQCARD-700, made by National InstrumentsCorporation). A thermal lens signal fetched into the notebook computerwas displayed on a display screen of the above-described notebookcomputer by software (LABVIEW 5.0, made by National InstrumentsCorporation), and signal values and time-dependent changes of the signalvalues were saved (all are not shown).

Furthermore, an automatic positioning stage (MINI-60X MINI-5P, made bySIGMA KOKI CO., LTD.) which can perform alignment in the direction of anoptical axis in a 1-micrometer level of resolution was used for a stageon which the sample cell 16 was placed and which is not shown.

The adjustment of an optical system was performed in the same procedureas the example 1, all the optics except the collimator lens 21 for probelight were fixed with adhesives on a box 59 made from aluminum afteradjustment, and were integrated (unitized).

Next, measurement procedure of a sample will be described. A glass cellwith the optical path length of 50 μm (AB20, made by GL Sciences, Inc.)was used as the sample cell 16, and this is placed on a stage, which isnot shown, to be fixed. Then, the stage was moved in the direction of anoptical axis, a boundary between air and glass was found with monitoringthe operation result of outputs of the quadrant photodiode 55 by thepersonal computer which is not shown, and thermal lens measurement wasperformed at a location moved therefrom by certain length.

The operation result at the time of moving the stage in the depthdirection is shown in FIG. 6. A region shown by symbol a in a graph inFIG. 6 shows that the sample cell 16 is far from a focal point of theexcitation light by the condenser lens 15, and a region shown by symbolc shows conversely that they are too close. A point shown by symbol bwhich crosses a baseline shows that the boundary between air and glassand a focal point of the excitation light coincide completely.

The alignment accuracy of the sample cell 16 at this time determines thealignment accuracy at the time of finally aligning the sample cell 16with the measuring point of the thermal lens. In this case, it was shownfrom the measurement result that the alignment in the accuracy of 2 μmor less was possible. Since a thermal lens signal changes about 2% if alocation of the sample cell 16 shifts by 5 μm, in the POC analysis etc.,where about 1% of accuracy is usually required, as seen from the resultdescribed later, it can be said that the photothermal spectroscopicanalyzer of this example has alignment accuracy required for thermallens measurement.

The measurement result of xylene cyanol by using the photothermalspectroscopic analyzer of this example will be described. The detectionlimit of an absorbance was 1.0×10⁻⁵ (Abs.), and similarly to the example1, the photothermal spectroscopic analyzer of this example was small andhighly sensitive in comparison with conventional technology. Inaddition, in this example, the distance from a sample to a pinhole was10 cm, and the size of the whole optical system was 15 cm D×15 cm W×15cm H. Therefore, it is the size of being easily carried.

INDUSTRIAL APPLICABILITY

Thus, a photothermal spectroscopic analyzer of the present invention isequipped with all the requirements as an apparatus, performing a POCanalysis etc., such as small size, inexpensiveness, high sensitivity,high accuracy, maintenance-free performance, short start-up time, andpossibility of automatic measurement.

1. A photothermal spectroscopic analyzer in which a probe light isincident on a thermal lens generated in a sample by incidence of anexcitation light, and for analyzing the sample on the basis of a changein the probe light by the thermal lens in that case, comprising: a lightsource of the excitation light which comprises semiconductor laserbeam-emitting means; a light source of the probe light which comprisesanother semiconductor laser beam-emitting means, wherein a condenserlens which focuses the excitation light in the sample and a condenserlens which focuses the probe light in the thermal lens are made to be acommon lens; at least one detection means of detecting a change in theprobe light by the thermal lens; and rounding means between at least thelight source of the excitation light or the light source of the probelight, wherein the condenser lens brings the cross sectional geometry ofat least one semiconductor laser beam emitted from the light sourcesinto approximately the shape of a circle, wherein, when a transmissionmeans, for allowing a part of the probe light which is changed by thethermal lens transmit, is provided between the sample and the at leastone detection means, a distance in a direction of an optical axisbetween the transmission means and the sample is set at 10 cm or less,and a distance in the direction of an optical axis between the at leastone detection means and the sample is set at 10 cm or less when atransmission means is not provided, and further a beam diameter in focalpoints of the excitation light and the probe light which are focusedwith the condenser lens, is 0.2 to 50 μm.
 2. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; at leastone detection means of detecting a change in the probe light by thethermal lens; and astigmatism correction means between at least thelight source of the excitation light or the light source of the probelight, wherein the condenser lens reduces the astigmatism of thesemiconductor laser beam, emitted from the light source of theexcitation light or the probe light, wherein, when a transmission means,for allowing a part of the probe light which is changed by the thermallens transmit, is provided between the sample and the at least onedetection means, a distance in a direction of an optical axis betweenthe transmission means and the sample is set at 10 cm or less, and adistance in the direction of an optical axis between the at least onedetection means and the sample is set at 10 cm or less when atransmission means is not provided, and further a beam diameter in focalpoints of the excitation light and the probe light which are focusedwith the condenser lens, is 0.2 to 50 μm.
 3. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; at leastone detection means of detecting a change in the probe light by thethermal lens; at least one collimator lens where a semiconductor laserbeam emitted from the light source of the excitation light is incident,or where a semiconductor laser beam emitted from the light source of theprobe light is incident; focal point adjustment means in the at leastone collimator lens for adjusting a focal point of the semiconductorlaser beam by changing a distance in the direction of an optical axisbetween the at least one collimator lens and the light source of theexcitation light or the probe light; means for adjusting a distancebetween at least one of focal points of the excitation light and theprobe light; and a sample cell which contains the sample, wherein theadjusting means utilizes light reflected from the sample cells, wherein,when a transmission means, for allowing a part of the probe light whichis changed by the thermal lens transmit, is provided between the sampleand the at least one detection means, a distance in a direction of anoptical axis between the transmission means and the sample is set at 10cm or less, and a distance in the direction of an optical axis betweenthe at least one detection means and the sample is set at 10 cm or lesswhen a transmission means is not provided, and further a beam diameterin focal points of the excitation light and the probe light which arefocused with the condenser lens, is 0.2 to 50 μm.
 4. The photothermalspectroscopic analyzer according to claim 1, further comprisingastigmatism correction means between at least the light source of theexcitation light or the light source of the probe light, wherein thecondenser lens reduces the astigmatism of at least one of thesemiconductor laser beams emitted from the light sources.
 5. Thephotothermal spectroscopic analyzer according to claim 1, wherein thelight source of the excitation light and the light source of the probelight are semiconductor laser beam-emitting means whose output iscontrollable.
 6. The photothermal spectroscopic analyzer according toclaim 1, wherein a wavelength of the excitation light is in a range of400 to 700 nm.
 7. The photothermal spectroscopic analyzer according toclaim 1, wherein the light source of the excitation light is asemiconductor laser beam-emitting means which is adapted to beelectrically modulated.
 8. The photothermal spectroscopic analyzeraccording to claim 1, further comprising signal extraction means whichextracts signals by synchronous detection.
 9. The photothermalspectroscopic analyzer according to claim 1, further comprising meansfor adjusting a distance between at least one of focal points of theexcitation light and the probe light; and a sample cell which containsthe sample, wherein the adjusting means utilizes light reflected fromthe sample cell.
 10. The photothermal spectroscopic analyzer accordingto claim 2, wherein the light source of the excitation light and thelight source of the probe light are semiconductor laser beam-emittingmeans which output is controllable.
 11. The photothermal spectroscopicanalyzer according to claim 2, wherein a wavelength of the excitationlight is in a range of 400 to 700 nm.
 12. The photothermal spectroscopicanalyzer according to claim 2, wherein the light source of theexcitation light is a semiconductor laser beam-emitting means which isadapted to be electrically modulated.
 13. The photothermal spectroscopicanalyzer according to claim 2, further comprising signal extractionmeans which extracts signals by synchronous detection.
 14. Thephotothermal spectroscopic analyzer according to claim 2, furthercomprising means for adjusting a distance between at least one of focalpoints of the excitation light and the probe light; and a sample cellwhich contains the sample, wherein the adjusting means utilizes lightreflected from the sample cell.
 15. A photothermal spectroscopicanalyzer in which a probe light is incident on a thermal lens generatedin a sample by incidence of an excitation light, and for analyzing thesample on the basis of a change in the probe light by the thermal lensin that case, comprising: a light source of the excitation light whichcomprises semiconductor laser beam-emitting means; a light source of theprobe light which comprises another semiconductor laser beam-emittingmeans, wherein a condenser lens which focuses the excitation light inthe sample and a condenser lens which focuses the probe light in thethermal lens are made to be a common lens; at least one detection meansof detecting a change in the probe light by the thermal lens; means foradjusting a distance between at least one of focal points of theexcitation light and the probe light; and a sample cell which containsthe sample, wherein the adjusting means utilizes light reflected fromthe sample cell, wherein, when a transmission means, for allowing a partof the probe light which is changed by the thermal lens transmit, isprovided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm.
 16. A photothermal spectroscopic analyzer in which a probelight is incident on a thermal lens generated in a sample by incidenceof an excitation light, and for analyzing the sample on the basis of achange in the probe light by the thermal lens in that case, comprising:a light source of the excitation light which comprises semiconductorlaser beam-emitting means; a light source of the probe light whichcomprises another semiconductor laser beam-emitting means, wherein acondenser lens which focuses the excitation light in the sample and acondenser lens which focuses the probe light in the thermal lens aremade to be a common lens; at least one detection means of detecting achange in the probe light by the thermal lens; at least one collimatorlens where a semiconductor laser beam emitted from the light source ofthe excitation light is incident, or where a semiconductor laser beamemitted from the light source of the probe light is incident; androunding means between at least the light source of the excitation lightor the light source of the probe light, wherein the condenser lensbrings a cross sectional geometry of at least one semiconductor laserbeam emitted from the light sources into approximately the shape of acircles, wherein, when a transmission means, for allowing a part of theprobe light which is changed by the thermal lens transmit, is providedbetween the sample and the at least one detection means, a distance in adirection of an optical axis between the transmission means and thesample is set at 10 cm or less, and a distance in the direction of anoptical axis between the at least one detection means and the sample isset at 10 cm or less when a transmission means is not provided, andfurther a beam diameter in focal points of the excitation light and theprobe light which are focused with the condenser lens, is 0.2 to 50 μm.17. A photothermal spectroscopic analyzer in which a probe light isincident on a thermal lens generated in a sample by incidence of anexcitation light, and for analyzing the sample on the basis of a changein the probe light by the thermal lens in that case, comprising: a lightsource of the excitation light which comprises semiconductor laserbeam-emitting means; a light source of the probe light which comprisesanother semiconductor laser beam-emitting means, wherein a condenserlens which focuses the excitation light in the sample and a condenserlens which focuses the probe light in the thermal lens are made to be acommon lens; at least one detection means of detecting a change in theprobe light by the thermal lens; at least one collimator lens where asemiconductor laser beam emitted from the light source of the excitationlight is incident, or where a semiconductor laser beam emitted from thelight source of the probe light is incident; and astigmatism correctionmeans between at least the light source of the excitation light or thelight source of the probe light, wherein the condenser lens reduces theastigmatism of at least one of the semiconductor laser beams emittedfrom the light sources, wherein, when a transmission means, for allowinga part of the probe light which is changed by the thermal lens transmit,is provided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm.
 18. A photothermal spectroscopic analyzer in which a probelight is incident on a thermal lens generated in a sample by incidenceof an excitation light, and for analyzing the sample on the basis of achange in the probe light by the thermal lens in that case, comprising:a light source of the excitation light which comprises semiconductorlaser beam-emitting means; a light source of the probe light whichcomprises another semiconductor laser beam-emitting means, wherein acondenser lens which focuses the excitation light in the sample and acondenser lens which focuses the probe light in the thermal lens aremade to be a common lens; at least one detection means of detecting achange in the probe light by the thermal lens; at least one collimatorlens where a semiconductor laser beam emitted from the light source ofthe excitation light is incident, or where a semiconductor laser beamemitted from the light source of the probe light is incident; means foradjusting a distance between at least one of focal points of theexcitation light and the probe light; and a sample cell which containsthe sample, wherein the adjusting means utilizes light reflected fromthe sample cell, wherein, when a transmission means, for allowing a partof the probe light which is changed by the thermal lens transmit, isprovided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm.
 19. A photothermal spectroscopic analyzer in which a probelight is incident on a thermal lens generated in a sample by incidenceof an excitation light, and for analyzing the sample on the basis of achange in the probe light by the thermal lens in that case, comprising:a light source of the excitation light which comprises semiconductorlaser beam-emitting means; a light source of the probe light whichcomprises another semiconductor laser beam-emitting means, wherein acondenser lens which focuses the excitation light in the sample and acondenser lens which focuses the probe light in the thermal lens aremade to be a common lens; at least one detection means of detecting achange in the probe light by the thermal lens; at least one collimatorlens where a semiconductor laser beam emitted from the light source ofthe excitation light is incident, or where a semiconductor laser beamemitted from the light source of the probe light is incident; focalpoint adjustment means in the at least one collimator lens for adjustinga focal point of the semiconductor laser beam by changing a distance inthe direction of an optical axis between the at least one collimatorlens and the light source of the excitation light or the probe light;and rounding means between at least the light source of the excitationlight or the light source of the probe light, wherein the condenser lensbrings a cross sectional geometry of at least one semiconductor laserbeam emitted from the light sources into approximately the shape of acircle, wherein, when a transmission means, for allowing a part of theprobe light which is changed by the thermal lens transmit, is providedbetween the sample and the at least one detection means, a distance in adirection of an optical axis between the transmission means and thesample is set at 10 cm or less, and a distance in the direction of anoptical axis between the at least one detection means and the sample isset at 10 cm or less when a transmission means is not provided, andfurther a beam diameter in focal points of the excitation light and theprobe light which are focused with the condenser lens, is 0.2 to 50 μm.20. A photothermal spectroscopic analyzer in which a probe light isincident on a thermal lens generated in a sample by incidence of anexcitation light, and for analyzing the sample on the basis of a changein the probe light by the thermal lens in that case, comprising: a lightsource of the excitation light which comprises semiconductor laserbeam-emitting means; a light source of the probe light which comprisesanother semiconductor laser beam-emitting means, wherein a condenserlens which focuses the excitation light in the sample and a condenserlens which focuses the probe light in the thermal lens are made to be acommon lens; at least one detection means of detecting a change in theprobe light by the thermal lens; at least one collimator lens where asemiconductor laser beam emitted from the light source of the excitationlight is incident, or where a semiconductor laser beam emitted from thelight source of the probe light is incident; focal point adjustmentmeans in the at least one collimator lens for adjusting a focal point ofthe semiconductor laser beam by changing a distance in the direction ofan optical axis between the at least one collimator lens and the lightsource of the excitation light or the probe light; and astigmatismcorrection means between at least the light source of the excitationlight or the light source of the probe light, wherein the condenser lensreduces the astigmatism of at least one of the semiconductor laser beamsemitted from the light sources, wherein, when a transmission means, forallowing a part of the probe light which is changed by the thermal lenstransmit, is provided between the sample and the at least one detectionmeans, a distance in a direction of an optical axis between thetransmission means and the sample is set at 10 cm or less, and adistance in the direction of an optical axis between the at least onedetection means and the sample is set at 10 cm or less when atransmission means is not provided, and further a beam diameter in focalpoints of the excitation light and the probe light which are focusedwith the condenser lens, is 0.2 to 50 μm.
 21. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; and atleast one detection means of detecting a change in the probe light bythe thermal lens; wherein, when a transmission means, for allowing apart of the probe light which is changed by the thermal lens transmit,is provided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm, wherein the light source of the excitation light and thelight source of the probe light are semiconductor laser beam-emittingmeans whose output is controllable, and wherein a wavelength of theexcitation light is in a range of 400 to 700 nm.
 22. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; and atleast one detection means of detecting a change in the probe light bythe thermal lens; wherein, when a transmission means, for allowing apart of the probe light which is changed by the thermal lens transmit,is provided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm, wherein the light source of the excitation light and thelight source of the probe light are semiconductor laser beam-emittingmeans whose output is controllable, and wherein the light source of theexcitation light is a semiconductor laser beam-emitting means which isadapted to be electrically modulated.
 23. A photothermal spectroscopicanalyzer in which a probe light is incident on a thermal lens generatedin a sample by incidence of an excitation light, and for analyzing thesample on the basis of a change in the probe light by the thermal lensin that case, comprising: a light source of the excitation light whichcomprises semiconductor laser beam-emitting means; a light source of theprobe light which comprises another semiconductor laser beam-emittingmeans, wherein a condenser lens which focuses the excitation light inthe sample and a condenser lens which focuses the probe light in thethermal lens are made to be a common lens; at least one detection meansof detecting a change in the probe light by the thermal lens; andwherein, when a transmission means, for allowing a part of the probelight which is changed by the thermal lens transmit, is provided betweenthe sample and the at least one detection means, a distance in adirection of an optical axis between the transmission means and thesample is set at 10 cm or less, and a distance in the direction of anoptical axis between the at least one detection means and the sample isset at 10 cm or less when a transmission means is not provided, andfurther a beam diameter in focal points of the excitation light and theprobe light which are focused with the condenser lens, is 0.2 to 50 μm,and wherein the light source of the excitation light and the lightsource of the probe light are semiconductor laser beam-emitting meanswhose output is controllable.
 24. A photothermal spectroscopic analyzerin which a probe light is incident on a thermal lens generated in asample by incidence of an excitation light, and for analyzing the sampleon the basis of a change in the probe light by the thermal lens in thatcase, comprising: a light source of the excitation light which comprisessemiconductor laser beam-emitting means; a light source of the probelight which comprises another semiconductor laser beam-emitting means,wherein a condenser lens which focuses the excitation light in thesample and a condenser lens which focuses the probe light in the thermallens are made to be a common lens; at least one detection means ofdetecting a change in the probe light by the thermal lens; means foradjusting a distance between at least one of focal points of theexcitation light and the probe light; and a sample cell which containsthe sample, wherein the adjusting means utilizes light reflected fromthe sample cells, wherein, when a transmission means, for allowing apart of the probe light which is changed by the thermal lens transmit,is provided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm, and wherein the light source of the excitation light andthe light source of the probe light are semiconductor laserbeam-emitting means whose output is controllable.
 25. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; and atleast one detection means of detecting a change in the probe light bythe thermal lens; wherein, when a transmission means, for allowing apart of the probe light which is changed by the thermal lens transmit,is provided between the sample and the at least one detection means, adistance in a direction of an optical axis between the transmissionmeans and the sample is set at 10 cm or less, and a distance in thedirection of an optical axis between the at least one detection meansand the sample is set at 10 cm or less when a transmission means is notprovided, and further a beam diameter in focal points of the excitationlight and the probe light which are focused with the condenser lens, is0.2 to 50 μm, wherein a wavelength of the excitation light is in a rangeof 400 to 700 nm, and wherein the light source of the excitation lightis a semiconductor laser beam-emitting means which is adapted to beelectrically modulated.
 26. A photothermal spectroscopic analyzer inwhich a probe light is incident on a thermal lens generated in a sampleby incidence of an excitation light, and for analyzing the sample on thebasis of a change in the probe light by the thermal lens in that case,comprising: a light source of the excitation light which comprisessemiconductor laser beam-emitting means; a light source of the probelight which comprises another semiconductor laser beam-emitting means,wherein a condenser lens which focuses the excitation light in thesample and a condenser lens which focuses the probe light in the thermallens are made to be a common lens; at least one detection means ofdetecting a change in the probe light by the thermal lens; and signalextraction means which extracts signals by synchronous detection,wherein, when a transmission means, for allowing a part of the probelight which is changed by the thermal lens transmit, is provided betweenthe sample and the at least one detection means, a distance in adirection of an optical axis between the transmission means and thesample is set at 10 cm or less, and a distance in the direction of anoptical axis between the at least one detection means and the sample isset at 10 cm or less when a transmission means is not provided, andfurther a beam diameter in focal points of the excitation light and theprobe light which are focused with the condenser lens, is 0.2 to 50 μm,and wherein a wavelength of the excitation light is in a range of 400 to700 nm.
 27. A photothermal spectroscopic analyzer in which a probe lightis incident on a thermal lens generated in a sample by incidence of anexcitation light, and for analyzing the sample on the basis of a changein the probe light by the thermal lens in that case, comprising: a lightsource of the excitation light which comprises semiconductor laserbeam-emitting means; a light source of the probe light which comprisesanother semiconductor laser beam-emitting means, wherein a condenserlens which focuses the excitation light in the sample and a condenserlens which focuses the probe light in the thermal lens are made to be acommon lens; at least one detection means of detecting a change in theprobe light by the thermal lens; means for adjusting a distance betweenat least one of focal points of the excitation light and the probelight; and a sample cell which contains the sample, wherein theadjusting means utilizes light reflected from the sample cell, wherein,when a transmission means, for allowing a part of the probe light whichis changed by the thermal lens transmit, is provided between the sampleand the at least one detection means, a distance in a direction of anoptical axis between the transmission means and the sample is set at 10cm or less, and a distance in the direction of an optical axis betweenthe at least one detection means and the sample is set at 10 cm or lesswhen a transmission means is not provided, and further a beam diameterin focal points of the excitation light and the probe light which arefocused with the condenser lens, is 0.2 to 50 μm, and wherein awavelength of the excitation light is in a range of 400 to 700 nm.
 28. Aphotothermal spectroscopic analyzer in which a probe light is incidenton a thermal lens generated in a sample by incidence of an excitationlight, and for analyzing the sample on the basis of a change in theprobe light by the thermal lens in that case, comprising: a light sourceof the excitation light which comprises semiconductor laserbeam-emitting means; a light source of the probe light which comprisesanother semiconductor laser beam-emitting means, wherein a condenserlens which focuses the excitation light in the sample and a condenserlens which focuses the probe light in the thermal lens are made to be acommon lens; at least one detection means of detecting a change in theprobe light by the thermal lens; and signal extraction means whichextracts signals by synchronous detection, wherein, when a transmissionmeans, for allowing a part of the probe light which is changed by thethermal lens transmit, is provided between the sample and the at leastone detection means, a distance in a direction of an optical axisbetween the transmission means and the sample is set at 10 cm or less,and a distance in the direction of an optical axis between the at leastone detection means and the sample is set at 10 cm or less when atransmission means is not provided, and further a beam diameter in focalpoints of the excitation light and the probe light which are focusedwith the condenser lens, is 0.2 to 50 μm, and wherein a light source ofthe excitation light is a semiconductor laser beam-emitting means whichis adapted to be electrically modulated.
 29. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; at leastone detection means of detecting a change in the probe light by thethermal lens; means for adjusting a distance between at least one offocal points of the excitation light and the probe light; and a samplecell which contains the sample, wherein the adjusting means utilizeslight reflected from the sample cell, wherein, when a transmissionmeans, for allowing a part of the probe light which is changed by thethermal lens transmit, is provided between the sample and the at leastone detection means, a distance in a direction of an optical axisbetween the transmission means and the sample is set at 10 cm or less,and a distance in the direction of an optical axis between the at leastone detection means and the sample is set at 10 cm or less when atransmission means is not provided, and further a beam diameter in focalpoints of the excitation light and the probe light which are focusedwith the condenser lens, is 0.2 to 50 μm, and wherein a light source ofthe excitation light is a semiconductor laser beam-emitting means whichis adapted to be electrically modulated.
 30. A photothermalspectroscopic analyzer in which a probe light is incident on a thermallens generated in a sample by incidence of an excitation light, and foranalyzing the sample on the basis of a change in the probe light by thethermal lens in that case, comprising: a light source of the excitationlight which comprises semiconductor laser beam-emitting means; a lightsource of the probe light which comprises another semiconductor laserbeam-emitting means, wherein a condenser lens which focuses theexcitation light in the sample and a condenser lens which focuses theprobe light in the thermal lens are made to be a common lens; at leastone detection means of detecting a change in the probe light by thethermal lens; signal extraction means which extracts signals bysynchronous detection; means for adjusting a distance between at leastone of focal points of the excitation light and the probe light; and asample cell which contains the sample, wherein the adjusting meansutilizes light reflected from the sample cell, wherein, when atransmission means, for allowing a part of the probe light which ischanged by the thermal lens transmit, is provided between the sample andthe at least one detection means, a distance in a direction of anoptical axis between the transmission means and the sample is set at 10cm or less, and a distance in the direction of an optical axis betweenthe at least one detection means and the sample is set at 10 cm or lesswhen a transmission means is not provided, and further a beam diameterin focal points of the excitation light and the probe light which arefocused with the condenser lens, is 0.2 to 50 μm.